78' 280Z stumbles under throttle application

[Virto]

Hey folks - I've recently revived my 280Z and am working to get it back on the road.

I've drained and replaced the old fuel - there was some sediment present, but I was surprised at how little.

The car turns over and starts easily, and idles like a champ, hovering around 850-900 RPM (it's an automatic, just fyi). However, when throttle is applied, power drops, the car will rev to 1500-3000 RPM or thereabouts and then pop, stutter and basically drop dead back to idle. The car never dies during this time.

The existing fuel pump wails like a banshee. I'm not sure if it's an OEM pump or an aftermarket junker. I do have an aftermarket pump on-hand for temporary use, as I don't have the cash for an OEM pump at this time. But trust me, I'm aware of the opinions on the aftermarket units...

Obviously, it's not drivable in this state, but it's enough that I can putt it around the driveway and garage while I work on it. It's easier to see in the sun, after all.

I'm compiling a list of tests and options. My tool selection is limited and I no longer have my vac or fuel pressure gauges, so I'll need to replace those at the least. Here's what I'm looking at so far:

Replace fuel filter (needs to be done anyway)

Perform vac test, possibly yogurt-cup option

Perform fuel pressure test

Some people have mentioned that the throttle valve switch has been the cause of stumbling like this. The FSM states that it can be continuity tested but you have to judge degrees of movement and it all sounds complicated. Is there a simple way to test this switch, like running the car with the harness disconnected?

When the car stumbles, it voices its displeasure, and sounds like it's backfiring under the hood - I'm pretty confident than my downpipe is rusted out, and that equal parts of the exhaust end up under the hood as that shoot out the back.

I've tried to capture this in a couple of videos that I'll compress and upload tonight when I'm home. They are fairly poor quality, but might be better than nothing.

[madkaw]

If the fuel pump is screaming- it yelling for help!

My zx turbo screamed when the fuel pressure was too high from an obstruction which will make things run lean and pop and ect....

[Virto]

I assumed it was just an outward sign of pump failure. It would certainly be nice if the pump itself wasn't an issue.

Was your obstruction past the pump or in the tank?

I'll be posting two vids, one standing by the engine bay working the throttle by hand and another from the cabin. In the cabin video, you can clearly hear the pump droning.

[siteunseen]

I'd bet the fuel filter is clogged. Walmart has one that's close to Nissan's for about $10 if I remember right, it's a Fram. I used one on my '77 for a couple of months when I first bought the car.

[Virto]

I'm positive that it's due for replacement at this point, period. O'Rileys carries both Fram and Wix replacements, I just hadn't picked one up before I did the water pump yesterday.

I might be able to snag one on lunch today.

[ZCurves]

Replace the fuel filter up by the engine, then remove the Fuel Pump and check the small screen filter on the inlet. Finally, buy a cheap plastic see-thru filter (3/8") and place between the tank and the fuel pump. Also could take a look at the Fuel Pressure Regulator.

[Virto]

I snagged a new under-hood filter on lunch. I've got that whole "add a little clear Fram between the tank and pump" article bookmarked already.

I'm not sure if the pump on the car is OEM, although it seems that most mechanical parts are - and not just OEM, but original.

I'll look into the FPR after I get a pressure reading.

[Virto]

Rain is heading in, but had plenty of time (I thought) to simply swap out the fuel filter.

The screw that tightens the bracket is immovable, but very soft. I knew I'd just round the whole thing out if I wasn't careful, so I gave up, soaked the hell out of it with ATF/Acetone and I'll try again tomorrow or so. Once I get it out, I'll probably replace it with a similarly sized bolt so I don't have to worry about it being an issue again.

[Virto]

OK attached are the vids I promised earlier. The sound is...poor. And the leaking exhaust drowns out a lot of the noise you're listening for, ie - the stumble, but it should still be apparent.

The in-cabin vid features my fuel pump whine - it's impossible to miss.

I tried to loosen the fuel filter bracket screw again tonight but no dice. I hit it with more acetone/ATF mix and I'll try again later in the week.

Thanks for the help, fellas.

Z Stall in car | Flickr - Photo Sharing!

Z stall enginebay | Flickr - Photo Sharing!

[siteunseen]

I would take the whole bracket off the car, after removing the hoses, put it on a bench and use a good pair of Vise Grips. 2 10mm bolts hold it on.

[Virto]

I've considered that as well. If the stupid screw was hex-head or, I don't know...maybe just a BOLT it would never have been an issue. I'll probably replace it with a bolt for ease of use in the future.

[FastWoman]

I think it sounds like an extreme lean condition. If you pull off the vacuum line to the fuel pressure regulator and block the little hose with your finger, does your engine still backfire when you hit the throttle?